Algae - Types & Examples, Defination

Characteristics of Algae

Algae represent a simple, autotrophic organism capable of generating energy from sunlight through photosynthesis in algae. It may be unicellular microalgae or multicellular forms like seaweeds. Besides their existence in different kinds of environments, algae also play an essential role in oxygen production and ecosystem balance.

Some general characteristics of algae are:

• Algae are chlorophyllous and photosynthetic in nature.

• They are found in a wide variety of habitats. Some may be exclusively freshwater, while others can be perfectly saltwater species.

• Algae reproduce both sexually and asexually, although the latter method is their main mode of reproduction.

• The structure of algae is a simple unicellular, filamentous, sheet‑like, or branched thallus.

• Algae exhibit different colours because of the occurrence of the various pigments present: green algae, brown algae, or red algae.

• It includes unicellular forms like diatoms and dinoflagellates, and large kelp forests.

Also Read:

• Algae: Characteristics and Classification MCQ

• Biological Classification

• Angiosperms

Types of Algae

The types of algae are classified into major groups: green algae, red algae, brown algae, and blue‑green algae (cyanobacteria). Each group has unique pigments, structures, and ecological roles. Some algae are unicellular, like diatoms and dinoflagellates, while others form large kelp forests. Studying the characteristics of algae and their diversity is important in biology, especially under the Plant Kingdom algae for NEET and Class 11 exams. The classification of the types of algae is outlined as follows:

Chlorophyta (Green Algae)

• Range from simple organisms such as Chlamydomonas to complex forms.

• They contain chloroplasts with chlorophylls A and B.

• Cell walls are made of cellulose.

• Found in moist terrestrial habitats (such as soils and rocks) and freshwater.

• Example- Volvox, Chlamydomonas, Spirogyra. Ulva (sea lettuce)

Phaeophyta (Brown Algae)

• Fucoxanthin is a pigment that gives brown algae seaweeds their brown or olive colour.

• They are large, multicellular forms like kelp.

• Common in cool coastal environments like coastal rocks

• Have kelp beds with a high concentration of nutrients.

• Examples- Sargassum, Fucus (Rockweed), Laminaria (Kelp)

Rhodophyta (Red Algae)

• Rhodophyta are characterised by their red to purplish colour due to phycoerythrin pigment.

• They are multicellular algae predominantly found in marine habitats.

• Red algae thrive in various marine environments, forming large beds or reefs.

• Examples- Gelidium, Porphyra (Nori), Corallina

Blue-Green Algae (Cyanobacteria)

• Also known as cyanobacteria are a group of photosynthetic algae

• They can exist as single cells or form multicellular colonies.

• Characterised by their blue-green colouration due to chlorophyll a and the pigment phycocyanin.

• Can be found in a variety of aquatic environments, including freshwater lakes, ponds, rivers, and aquatic ecosystems.

• Examples- Anabaena, Microcystis, Nostoc

Other Types of Algae

Diatoms: Unicellular algae encased in silica walls (frustule), exhibiting diverse shapes like cylindrical and star-like forms. They are essential for converting carbon dioxide into oxygen. They are found in both freshwater and marine environments. Diatoms dominate nutrient-rich areas and form an important part of the aquatic food chain.

Examples- Navicula, Diatomaceous Earth

Dinoflagellates: Unicellular algae possessing two flagella, allowing them to swim. They can be autotrophic, photosynthetic, or heterotrophic. These algae are prevalent in both marine and freshwater environments and can cause harmful algal blooms.

Examples: Symbiodinium, Gonyaulax

Examples of Algae

Some notable examples of algae include:

• Chlorella: A unicellular green alga known for its high nutritional value.

• Spirulina: A cyanobacterium that is often consumed as a health supplement.

• Nori: A red alga used in sushi.

• Ulva (Sea Lettuce): A green alga eaten as food in coastal regions.

• Laminaria (Kelp): A brown alga used in medicine and the food industry.

• Sargassum: A floating brown alga forming large mats in oceans.

• Gelidium: A red alga used in agar production.

• Navicula (Diatoms): Unicellular algae with silica walls, major oxygen producers.

• Dinoflagellates (e.g., Gonyaulax): Unicellular algae that can cause algal blooms.

• Anabaena: A blue‑green alga (cyanobacterium) known for nitrogen fixation.

Uses of Algae

Algae are important for both ecosystems and humans. They produce oxygen and absorb carbon dioxide. They form the base of the aquatic food chain. Beyond ecology, algae have wide applications, such as in food, medicine, and industry.

1. Food:

• Green algae (Ulva, Chlorella) are eaten as vegetables and supplements.

• Red algae (Nori, Gelidium) are used in sushi and agar production.

• Spirulina (cyanobacteria) is consumed worldwide as a health supplement, rich in protein and vitamins.

2. Medicine:

• Brown algae (Laminaria, Sargassum) are used in traditional medicine and modern drugs.

• Compounds from algae show antibacterial, antiviral, and antioxidant properties.

• Agar and carrageenan from red algae are used in medical labs.

3. Industry:

• Algae are used in cosmetics, fertilisers, and wastewater treatment.

• Diatoms with silica walls are used in filtration and polishing.

• Dinoflagellates contribute to bioluminescence research.

Algal Biofuel

Another use of algae is to produce biofuel. Lipids are produced by the cultivation of algae for biofuel. This renewable energy offers a sustainable substitute for fossil fuels. Algal biofuel has great potential because, in comparison to conventional crops, algae can develop quickly and effectively. It yields large amounts of algal biofuel per acre. Research shows algae as a promising solution for future energy needs.

MCQs on Algae for NEET

Question: Which one of the following shows isogamy with nonflagellated gametes?

1. Sargassum

2. Ectocarpus

3. Spirogyra

4. Chara

Correct Answer: 3) Spirogyra

Explanation:

Sexual reproduction in algae takes place through the fusion of two gametes. It can be of the following types:

1. Isogamous- Fusion of two gametes of similar in size, either flagellated or non-flagellated. Eg., Chlamydomonas(gametes are flagellated and similar in size) , (gametes are non-flagellated and similar in size).

2. Anisogamous- Fusion of two gametes of disimilar in sizSpirogyra e. Eg., Some species of Chlamydomonas, Ectocarpus secundus.

3. Oogamous- Fusion of small motile male gamete and large non-motile female gamete. Eg., Volvox, Fucus, Ectocarpus, Chara.

Hence, the correct answer is option 3) Spirogyra .

Question: Deepest algae in the sea are

1. Brown algae

2. Red algae

3. Green algae

4. Golden algae

Correct Answer: 2)Red algae

Explanation:

Phycocyanin-pigmented red algae live in the deepest parts of the ocean because they possess an extraordinary ability to absorb blue-green light, which passes through water more successfully than other wavelengths. Photosynthesis in low light occurs with the help of the pigment in red algae; hence, they can survive in deep-sea areas where light is scarce. Red algae can grow in greater depths than green and brown algae since the latter two do not have this adaptation.

Hence, the correct answer is option 2) Red algae

Question: Which algal groups have similarity in pigment composition?

1. Red algae and brown algae

2. Green algae and blue-green algae

3. Kelps and diatoms

4. Diatoms and euglenoids

Correct Answer:3) Kelps and diatoms

Explanation:

Pigments in various groups of Algae: Red algae: chlorophyll a, d, and phycoerythrin. Brown algae: chlorophyll a, c, and fucoxanthin. Fucoxanthin (brown pigment)- Kelps and diatoms The two main types of pigment found in the euglenoids are the green chlorophyll and the orange-red carotenoids.

Hence, the correct answer is option 3) Kelps and diatoms

Practice More:

• Chlorophyceae or Green Algae MCQ

• Phaeophyceae or Brown Algae MCQ

• Rhodophyceae or Red Algae MCQ

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